The present invention relates generally to a diagnostic medical imaging apparatus that employs a near-infrared laser as a radiation source and more particularly to a method and apparatus for using a biochemical marker that selectively binds to cancer cells and emits radiation when excited different from the apparatus laser beam to provide a positive identification of the cancer site in a reconstructed image of the scanned tissue.
Cancer of the breast is a major cause of death among the American female population. Effective treatment of this disease is most readily accomplished following early detection of malignant tumors. Major efforts are presently underway to provide mass screening of the population for symptoms of breast tumors. Such screening efforts will require sophisticates, automated equipment to reliably accomplish the detection process.
The x-ray absorption density resolution of present photographic x-ray methods is insufficient to provide reliable early detection of malignant tumors. Research has indicated that the probability of metastasis increases sharply for breast tumors over 1 cm in size. Tumors of this size rarely produce sufficient contrast in a mammogram to be detectable. To produce detectable contrast in photographic mammogram 2-3 cm dimensions are required. Calcium deposits used for inferential detection of tumors in conventional mammography also appear to be associated with tumors of large size. For these reasons, photographic mammography has been relatively ineffective in the detection of this condition.
Most mammographic apparatus in use today in clinics and hospitals require breast compression techniques which are uncomfortable at best and in many cases painful to the patient. In addition, x-rays constitute ionizing radiation which injects a further risk factor into the use of mammographic techniques as most universally employed.
Ultrasound has also been suggested as in U.S. Pat. No. 4,075,883, which requires that the breast be immersed in a fluid-filled scanning chamber U.S. Pat. No. 3,973,126 also requires that the breast be immersed in a fluid-filled chamber for an x-ray scanning technique.
In recent times, the use of light and more specifically laser light to non-invasively peer inside the body to reveal the interior structure has been investigated. This techniques is called optical imaging. Optical imaging and spectroscopy are key components of optical tomography. Rapid progress over the past decade have brought optical tomography to the brink of clinical usefulness. Optical wavelength photons do not penetrate in vivo tissue in a straight line as do x-ray photons. This phenomena causes the light photons to scatter inside the tissue before the photons emerge out of the scanned sample.
Because x-ray photons propagation is essentially straight-line, relatively straight forward techniques based on the Radon transform have been devised to produce computed tomography images through use of computer algorithms. Multiple measurements are made through 360xc2x0 around the scanned object. These measurements, known as projections, are used to back-project the data to create an image representative of the interior of the scanned object.
In optical tomography, mathematical formulas and projection techniques have been devised to perform a reconstruction function somewhat similar to x-ray tomography. In order to perform an accurate reconstruction, the location of the points on the scanned object at which data are measured must be known.
In reviewing a reconstructed image of a tissue that has been optically scanned, there is a need to be able to identify the type of objects showing within the tissue. Once the object has been identified and its precise location determined, effective therapy is then initiated based on the photodynamic therapy drugs.
It is an object of the present invention to provide a laser imaging apparatus that uses a biochemical marker to provide a precise location of cancer cells within a tissue being scanned.
It is another object of the present to provide a laser imaging apparatus that uses a fluorophore that binds to cancer cells within a tissue being scanned to provide a precise location of the cancer cells by collecting the radiation intensity emitted by the fluorophore when excited by the laser beam of the apparatus.
It is still another object of the present invention to provide a laser imaging apparatus for imaging a lesion within a tissue and for providing the appropriate wavelength for a laser to activate a photodynamic therapy drug brought to the lesion by a biochemical marker.
It is another object of the present invention to provide a laser imaging apparatus for determining the shortest pathlength between the surface of the tissue and the location of the lesion to allow efficient irradiation by laser energy of a photodynamic therapy drug attached to the lesion.
It is also an object of the present invention to provide a laser imaging apparatus that can detect the presence and location of lesion within a tissue and at the same time providing therapy.
In summary, the present invention provides a method for reconstructing an image of a scanned object, comprising the steps of providing a source of laser beam; providing a biochemical marker that selectively binds to cancer cells within the tissue; directing the laser beam toward the object being scanned; orbiting the laser beam around the object; providing a plurality of sensors adapted to simultaneously detect the laser beam after passing through the object; and limiting the sensors to detect only the radiation released by the biochemical marker after having been activated by the laser beam.
The present invention also provides a method for activating a photodynamic therapy (PDT) drug attached to abnormal cells within a tissue, comprising the steps of providing a biochemical marker carrying a PDT drug within the tissue; scanning the tissue to locate the position of the abnormal cells; determining the shortest path length for a laser beam having a wavelength appropriate for the PDT drug; and directing the laser beam toward the abnormal cells to activate the PDT drug.
The present invention also provides an apparatus for imaging an object, comprising a scanning chamber for receiving therein an object being scanned; a source of laser beam disposed within the scanning chamber for impinging on the object being scanned, the laser beam being adapted to orbit around the object; an array of sensors disposed within the chamber, each of the sensors being adapted to detect radiation emanating from a biochemical marker attached to cancer cells; and a computer programmed to take the output of each detector at every location in the orbit around the object to reconstruct an image of the object.
These and other objects of the present invention will become apparent from the following detailed description.